The present invention pertains to cyanoacrylate adhesives which are cured using an activator compound having multiple amine functional groups thereon (a xe2x80x9cmulti-aminexe2x80x9d), to the cured products thereof and to novel multi-amine activator compounds. The invention also pertains to a method of bonding substrates, especially nonpolar substrates such as polyolefins, using cyanoacrylate adhesives activated with certain multi-amine compounds, to bonded assemblies produced thereby.
Compounds with a variety of highly branched architectures, such as xe2x80x9ccascade,xe2x80x9d xe2x80x9cdendrimer,xe2x80x9d xe2x80x9chyperbranchedxe2x80x9d and xe2x80x9ccomb-like,xe2x80x9d architectures, are known. As used herein, the terms xe2x80x9cmulti-amine cascade compounds,xe2x80x9d xe2x80x9cmulti-amine dendrimers,xe2x80x9d xe2x80x9cmulti-amine hyperbranched compoundsxe2x80x9d and xe2x80x9cmulti-amine comb-like compoundsxe2x80x9d refer to compounds having such branched architectures in which branching occurs via tertiary amine groups.
Cascade molecules are high molecular weight macromolecules with a very unique continuously branching structure emanating from a core unit. Formulae are characterized as having a geometrically increasing number of monomer derived branch units in each xe2x80x9cgenerationxe2x80x9d (the core being assigned generation 0, i.e. G0, and successive generations numbered sequentially, i.e. G1, G2, G3, etc). Idealized, such compounds are substantially monodisperse with all of the terminal groups being equidistant (measured through the chained bonds) from the core. However, frequently a given synthetic route will produce a distribution of macromolecules having branches of different lengths.
E. Buhleier, W. Wehner and F. Vxc3x6gtle, xe2x80x9cxe2x80x98Cascadexe2x80x99-and xe2x80x98Nonskid-Chain-likexe2x80x99 Synthesis of Molecular Cavity Topologies,xe2x80x9d Synthesis, 1978, pp 155-158, (incorporated herein by reference) reports that cascade poly(alkyleneamine) compounds may be obtained from Michael addition of acrylonitrile to a monoamine or diamine core molecule such as phenylmethyl amine and ethylenediamine, 1, 3,-di-(methylamino)benzene or 1,6-di(methylamino)pyridine, respectively, followed by reduction of the terminal nitrile groups to primary amine groups. Successive generations of such compounds, each increasing the number of branches on the molecule, are produced by repeating the Michael addition and nitrile reduction reactions on the previous generation product.
Multi-amine dendrimers, which may be considered to be substantially monodisperse cascade compounds, often with a generally spheroidal morphology may be prepared in a number of ways. In U.S. Pat. No. 5,610,268, incorporated herein by reference, poly(alkyleneamine) dendrimers are obtained by Michael additions of acrylonitrile or similar compounds to an active hydrogen functional core molecule such as 1,4-butanediamine, in like manner to the process of the E. Buhleier, W. Wehner and F. Vxc3x6gtle paper discussed above. Generation numbers of three or more are described in this patent.
Poly(alkylester) dendrimers branching out from tertiary amino groups are described in Coleshill, A., et al, Polymer Preprints, 38(1) 135 (4/1997), (also incorporated herein by reference.) In this reference the branch units are derived from 2-(di-(t-butyldimethylsilyloxyethyl))aminoacetic acid monomer. The core is a polyol such as 1,4-dihydroxybenzene or 1,4-butanediol. The first generation dendrimer is prepared by esterification reaction between the core hydroxy groups and monomer acid group, followed by removal of protecting t-butyldimethylsilyl groups to give the multi-amine dendrimer having terminal hydroxyl groups. Successive esterification reactions of the dendrimer with monomer acid followed by deprotection of the t-butyldimethylsilyl groups of the monomer give successive generations of this multi-amine dendrimer.
Poly(alkylamide) dendrimers branching out from tertiary amino groups are described in U.S. Pat. No. 4,507,466, also incorporated herein by reference. In this patent Michael addition of methyl acrylate to ammonia or a primary amine core, followed by displacement of the ester with a diamine, such as ethylene diamine, produces a first generation dendrimer with primary amine terminated amide functional branch units. Successive Michael additions with methyl acrylate and diamine displacement reactions give successive generations of this multi-amine dendrimer.
Hyperbranched compounds are polymeric materials, typically prepared in a single polymerization step, with a very high degree of branching resulting from the choice of monomer and/or polymerization mechanism employed. The monomer may be an ABn type monomer, where A and B represent different reactive groups capable of undergoing an addition or condensation reaction with each other and n represents an integer equal to or greater than 2. Idealized fully branched homopolymer structures are similar to dendrimers but in practice the polymer molecules prepared in this way are characterized by a higher polydispersity and a lower degree of branching than an analogous dendrimer. Hyperbranched architectures may also result from chain transfer processes in conventional addition or ring opening reactions. Poly(ethyleneimine), prepared by ring opening polymerization of aziridines, is an example of this type of molecule and is a multi-amine compound.
Multi-amine molecules having xe2x80x9ccomb-likexe2x80x9d architecture are characterized by a linear amine group-containing backbone with pendant side groups extending therefrom.
It has long been appreciated that cyanoacrylate adhesives give poor bonds when one or both substrates being bonded are nonpolar materials. This problem is particularly acute for polyolefin substrates and especially for low density polyethylene (LDPE). To improve bonding to such materials, a variety of primer activators have been employed with cyanoacrylate adhesives. Typically the activator is applied to one or both substrates neat or as a solution in a volatile solvent. The solvent, if present is dried and then the adhesive applied and the substrates promptly joined.
Organometallic compound primers for cyanoacrylate adhesives are described in JP 61-136567; U.S. Pat. No. 4,822,426; U.S. Pat. No. 5,110,392; U.S. Pat. No. 5,292,364 and Yang, J, et al., Primers for Adhesive Bonding to Polyolefins,xe2x80x9d J Applied Polymer Sci., 48, 359-370 (1993).
Amine, amine salt or other nitrogen compound primers for cyanoacrylate adhesives are described in U.S. Pat. No. 3,260,637 (various secondary and tertiary mono and diamine compounds); U.S. Pat. No. 4,814,427 (mixture of aldehyde and organic amine); U.S. Pat. No. 4,869,772 (diazabicyclo and triazabicyclo compounds); U.S. Pat. No. 4,979,993 (tertiary ammonium alkylcarboxylates); U.S. Pat. No. 5,079,098 (quaternary ammonium compounds); U.S. Pat. No. 5,133,823 (imidazole derivatives); U.S. Pat. No. 5,135,598 (ethylenically unsaturated amine polymerized before the adhesive is applied); U.S. Pat. No. 5,314,562 (ethylenediamine and certain derivatives thereof); U.S. Pat. No. 5,567,266 (organic amines in certain carriers); EP 0476203 B1 (certain tertiary propylene and butylene diamines); EP 0271675 (mixture of aldehyde and organic amine); McDonnell, P., xe2x80x9cBonding of Polyolefins with Cyanoacrylate Adhesives,xe2x80x9d Adhesion (London), 15, 69-79, (1991); Okamoto, Y., et al., xe2x80x9cBonding Non-Polar Plastics with Alkyl Cyanoacrylate Instant Adhesive,xe2x80x9d ANTEC""91 (49th Annu. Tech Conf.-Soc. Plast. Eng.), 1114-1117 (1991); Okamoto, Y., et al., xe2x80x9cPrimers for Bonding Polyolefin Substrates with Alkyl Cyanoacrylate Adhesive,xe2x80x9d J. Adhesion, 40, 81-91 (1993); and Yang, D., xe2x80x9cAnalysis of the Polyolefin/Trialkylamine Primer Interface,xe2x80x9d Surface and Interface Analysis, 20 407-415 (1993).
Heretofore 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) and tri-n-dodecylamine (TDA) have been found to be among the most useful polyolefin primer materials. These primers, however, give only a limited improvement in bond strength on the lowest energy surface materials, such as LDPE, and typically do not give bonds which fail by a substrate failure mode on LDPE. There is therefore a continued need for primer materials for cyanoacrylate adhesives which will give improved bonding to polyolefins, and in particular to LDPE.
The invention is directed to primer compositions for cyanoacrylate or related anionically polymerizable monomers. The primers employ a multi-amine compound in a volatile organic solvent. The multi-amine compound has at least three secondary or tertiary amine groups, at least one of which is-a tertiary amine group. The multi-amine compound also has at least three terminal and/or pendant aliphatic hydrocarbon groups of at least 4 carbon atoms in length thereon. The aliphatic hydrocarbon groups are suitably alkyl or alkenyl groups.
The primers of the invention give substantially improved bond strengths to cyanoacrylate adhesive bonded assemblies comprising a polyolefin substrate, such as a high density polyethylene, LDPE or polypropylene substrate. They give especially striking improvement when at least one of the substrates being bonded is LDPE.
The invention is also directed to cyanoacrylate adhesive compositions which include such multi-amine compounds, and to cured cyanoacrylate polymers and bonded assemblies produced by bringing an xcex1-cyanoacrylate monomer into contact with such a multi-amine compound.
The invention is also directed to (certain novel multi-amine compounds) which are characteristically terminated with C4 or higher alkyl or alkenyl groups. Such multi-amine compounds include the following: 
where Rxe2x80x2 is xe2x80x94CH2CH2xe2x80x94 or xe2x80x94CH2CH2CH2xe2x80x94; R2 is H or R3; the R3 groups are the same different C4-C22 alkyl, alkenyl, carboxyalkyl,carboxyalkenyl or xe2x80x94CH2CH2C(xe2x95x90O)OR4; and R4 is C4-C22 alkyl. Linear or branched poly(alkylenimine) having at least three terminal and/or pendent groups defined as for R3 are further multi-amine compounds of the invention.